An interstitial light assembly for photodynamic therapy in prostatic carcinoma

Objective To develop an interstitial laser light delivery system using mult iple optical fibres for photodynamic therapy (PDT) in the treatment of pros tate cancer. Patients and methods A laser beam was divided equally with a 1 x 4 fibre sp litter to deliver PDT simultaneously through four 2-cm long, flexible cylin drical optical diffusers. Biplanar transrectal ultrasonography (TRUS) and a template were used to position the optical fibres percutaneously. In vivo measurements of light penetration depth (1/mu(eff)) in prostate tissue were made in seven patients, using a sheathed isoprobe to measure light fluence rates at varying radial distances from the diffuser. The prostate was fixe d with stabilization needles to minimize displacement during needle placeme nt. Results The mean (SD, range) mu(eff) in the prostates of the seven patients was 0.35 (0.07, 0.22-0.44)mm(-1) which produced closely parallel slopes of light attenuation. However, there was up to a 10-fold variation in absolut e light levels at the same diffuser-detector separation distances amongst t he seven patients, probably caused by blood pooling around the diffuser lig ht source. A similar problem around the isoprobe detector was overcome by s heathing the probe in clear plastic tubing. By stabilizing the prostate, th e optical fibre positioning was precise to within 2 mm. Conclusion Although this light delivery and TRUS assembly were developed fo r clinical PDT in the prostate, the same instrumentation can be used reliab ly for in vivo light-penetration studies. Haemorrhage was unpredictable and highlighted one of the main problems which needs to be overcome.